Calcium metabolism in microgravity

Area of Science:

• Space medicine
• Bone metabolism
• Astronaut health

Background:

• Microgravity and immobilization lead to bone demineralization, a primary cause of space osteoporosis.
• Astronauts can experience 1%-1.6% bone mineral density reduction in key areas during 4.5-6 month missions, with potential losses up to 14% in the femoral neck.
• Space osteoporosis poses a significant risk for long-duration spaceflight, including missions to Mars.

Purpose of the Study:

• To investigate the effects of high calcium intake and vitamin D supplementation on calcium and bone metabolism during space missions.
• To compare the bone loss patterns in spaceflight to terrestrial conditions like postmenopausal osteoporosis and Anorexia Nervosa.
• To assess the efficacy of nutritional interventions in mitigating space osteoporosis.

Main Methods:

• Analysis of astronaut bone mineral density using Dual Energy X-ray Absorption (DEXA).
• Monitoring of bone turnover biomarkers during space missions.
• An experiment during the MIR 97 mission involving high calcium (>1000 mg/d) and vitamin D (650 IU/d) supplementation for 21 days in microgravity.

Main Results:

• Bone unloading in microgravity significantly impacts calcium and bone metabolism.
• High calcium and vitamin D intake in the MIR 97 mission resulted in elevated ionized calcium and decreased calcitriol levels.
• These nutritional interventions led to decreased bone formation and increased bone resorption markers, despite adequate intake.

Conclusions:

• Adequate calcium and vitamin D intake are mandatory for astronauts during space missions.
• Unlike on Earth, these supplements do not effectively counteract the development of space osteoporosis under microgravity conditions.
• Other factors like stress, nutrition, fluid shifts, and bone perfusion also contribute to space osteoporosis, requiring further investigation.